Python string replace the values

[Ganesh Pal]

MRAB  , Thanks for your solution it looks neat and best !


On Fri, Sep 1, 2017 at 11:14 PM, MRAB <python at mrabarnett.plus.com> wrote:

> On 2017-09-01 18:13, Ganesh Pal wrote:
>
>> In the fixed length string i.e "a0000",last 4 bits i.e "0000" should be
>> replaced by the user provided value ( the value is between 0001 + f f f f
>> )
>> . I intend to form  final_string  using a fixed_string and an user
>> provided
>>   user_string
>>
>>
>> Example:
>>
>> fixed_string = "a0000"
>> user_string ='1'
>>
>> final string = fixed_string  and  user_string
>>
>> Example :
>>
>>    "a0000" and "1" => a0001
>>
>>    "a0000" and "aa" => c00aa
>>
>>
>> PS :  "and" this is not logical and it's just for example
>>
>> If I concatenation using + or +=  or it's append the value at the end of
>> the string
>>
>> "a0000" + "1"    ===> expected was a0001
>>>>>
>>>> 'a00001'
>>
>>
>>
>>   I am on python 2.7 and Linux ,  any ideas that you recommend  to handle
>> this
>>
>> How long is user_string? len(user_string)
> Truncate fixed_string by that many characters: fixed_string[ :
> -len(user_string)]
>
> Then append the user_string: fixed_string[ : -len(user_string)] +
> user_string
>
> Example:
>
> >>> fixed_string = "a0000"
> >>> user_string ='1'
> >>> len(user_string)
> 1
> >>> fixed_string[ : -len(user_string)]
> 'a000'
> >>> fixed_string[ : -len(user_string)] + user_string
> 'a0001'
>
> Note: this won't work properly if len(user_string) == 0, so if that could
> happen, just skip it. (Appending an empty string has no effect anyway!)
> --
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>